Modern thermoplastic molding resin compositions, depending on the molecular composition of the polymer and on its molecular weight, offer the molder a range of materials with surprisingly good physical properties for use in difficult environments, such as at elevated temperatures. A number of such materials, however, require unusually high fabrication temperatures for efficient processing, such as melt temperatures above 600.degree. F. for injection molding. Because resin manufacturers are constrained to market only grades of resin that can be processed in available equipment, this constraint leads to practical compromises in ultimate physical properties. This problem can be better illustrated, for example, by reference to a specific type of polycarbonate resins.
2,2 bis-(p-hydroxyphenyl)propane polycarbonate (hereinafter referred to as bisphenol-A polycarbonate) is a well known thermoplastic polymer offering good thermal stability, excellent dimensional stability and resistance to creep under load. Injection molding grades of bisphenol-A polycarbonate have intrinsic viscosities (as measured in methylene chloride at 30.degree. C.) in the range of about 0.40 to 0.55 dl/g. A typical polymer in that viscosity range has a weight-average molecular weight of about 30,000, and a number-average molecular weight of about 11,000. The mechanical properties of bisphenol-A polycarbonate increase very rapidly with increased intrinsic viscosity until the intrinsic viscosity reaches about 0.40, and then taper off. The melt viscosity of the resin, however, increased rapidly at intrinsic viscosities greater than about 0.45, and at intrinsic viscosities of about 0.6 the melt viscosity is already sufficiently high that injection molding with complex molds becomes quite difficult. Practical commercial molding grades therefore must be constrained to molecular weights that provide a resin with sufficient fluidity at molding temperature but with less than maximum physical properties.
It has now been found that insertion of small quantities of cyclopentadiene or cyclopentadiene-type dicarboxylic acid groups with these resins brings about processing advantages without significant loss of properties.
The synthesis of 1:1 polyesters of dicyclopentadiene dicarboxylic acid with bis-(p-hydroxyphenyl)ether and with 2,2-bis-(p-hydroxyphenyl)propane is described by Mirva et al. in Bulletin of the Chemical Society of Japan, Vol. 50, No. 10, pp 2682-2685 (1977). These resins have been shown to undergo reversible thermal degradation in 10 wt. % nitrobenzene solution. A 1 wt. % solution does not show this behavior.
The use of dicyclopentadiene to reversibly cross-link polyisobutylene has been described by Kennedy and Castner in Journal of Polymer Science, Vol. 17, No. 7, page 2039 and page 2055 (1979). However no extension of the technology to the enhancement of the melt flow of thermoplastic resins is suggested.